This invention relates to vehicle seats.
In particular, the invention relates to a vehicle seat of the type in which a seat part, including a seat support and a back rest, is mounted on a base part by means of a suspension which is operative to guide the seat part for upward and downward movement relative to the base part between UP stop and DOWN stop positions. The suspension includes a biasing spring which acts between the base part and the seat part to couterbalance the weight of the seat part and seat occupant.
More particularly the invention concerns the type of suspension which is contained largely if not wholly between the seat part and the base part. An example of such a seat design can be found in our Simons et al U.S. Pat. No. 3,109,621 in which the suspension comprises two parallel spaced pairs of scissor linkages disposed respectively in vertical planes extending fore and aft of the seat, these linkages serving to constrain the movement of the seat to a vertical direction. One significant advantage of a seat suspension which is contained largely between the seat part and the base part is that it facilitates the provision of a back rest which is tiltable about an axis adjacent the bottom of the back rest. Such a back rest can be mounted on a parallel spaced pair of supporting arms which are pivoted at their lower ends to a frame incorporated in the seat part.
In a suspension seat, it is conventional to incorporate a shock absorber or vibration damper in the form of a cylinder containing vibration damping fluid and a piston movable along the axis of the cylinder by means of a piston rod emerging from one end of the cylinder. The movement of the piston is damped by causing the fluid to pass from one side of the piston to the other through a restricted leakage path. Such a damper is a long piece of equipment relative to the dimensions of the seat and is preferably connected at one end to the base part and at its opposite end to a position on the back rest well above the seat cushion. Difficulty however can arise if it is desired to tilt the back rest since the pivot axis of the back rest is close to the level of the seat support, and hence tilting of the back rest in a rearward direction would seriously contract the length of, and interfere with the operation of, a vibration damper directly connected to the back rest.